Adjustable seats are used in a wide variety of applications, ranging from residential chairs and sofas to driver and passenger seats used in vehicles, such as automobiles, airplanes, and trains. Such seats typically include a seat member and a back, with the position of at least one of these two elements being adjustable. For example, a position of the seat back may be adjustable to reconfigure the seat from an erect seated positioned to a supine reclined position. In some seats, the height and/or angle of the seat member may also be adjusted. Some seats include other adjustable members, e.g., leg rests, headrests, lumbar supports, or the like.
Power-actuated seats are becoming increasingly prevalent, particularly in automobiles and first-class and business-class seating on airplanes. Rather than requiring a user to manually adjust the positions of the elements of the seat, a power-assisted device, such as a mechanical or hydraulic actuator, or a series of such devices, is employed. A passenger may use buttons or control levers, which may be located on a common keyboard or console, to control the power-assisted devices to reconfigure the seat to meet his or her preferences.
The actuators of most power-actuated seats move the relevant member of a seat with the same force, regardless of the weight of the person seated in the seat. Since the force of the actuator must be sufficient to move the relevant seat element for the heaviest passenger, such constant-force actuators must be configured to operate at full force at all times. This can waste electricity and it may cause undue wear and tear on the actuator.
Reducing the force applied by the actuator to a level more commensurate with needs may also enhance safety of a power-actuated seat. For example, a child may inadvertently place one of his legs between the leg rest and the seat member of the seat. If the position of the seat member or the leg rest is adjusted, the child's leg may become pinned between the leg rest and the seat member. With a constant-force actuator, the actuator must move the seat member or the leg rest with sufficient force to move the seat member or leg rest against the weight of the heaviest accommodated passenger. If the force of the actuator were instead reduced to a level more appropriate for a lighter child, the force acting against the child's pinned leg could be reduced, reducing the likelihood of any injury to the child.
Efforts have been made to detect whether a passenger is seated in an automobile seat and disable deployment of an airbag or other supplemental restraint system if an automobile seat is unoccupied or is occupied by a small child. For example, U.S. Pat. No. 5,905,210 (O'Boyle et al.), U.S. Pat. No. 6,058,341 (Myers et al.), and U.S. Pat. No. 6,242,701 (Breed et al.), the teachings of each of which is incorporated herein by reference, all propose separate mechanisms which can be incorporated into an automobile passenger seat to respond to the weight of any passenger occupying the seat. These separate weighing mechanisms incorporated into the seats add weight and cost to the seat.
Some known automobile passenger weighing systems suffer from other drawbacks, as well. For example, some passenger seat weight sensors include one or more pads which employ force sensitive resistive films. The resistance values of most such films will change with temperature and can drift over time with a constant load on the film. Other automotive seats, such as the one proposed by Myers in U.S. Pat. No. 6,058,341, employ inflatable bladders. Operation of such inflatable bladders tends to vary with changes in ambient temperature and pressure. The fluid used to inflate such bladders may leak out or pass through the bladder wall through osmosis, which requires a mechanism for automatically replenishing the fluid within the bladder from time to time.
In aircraft seat applications, weight and electrical power are both at a premium. Airline passengers are coming to expect more and more amenities, particularly in first-class and business-class seating. These amenities include reading lights, video monitors for personal entertainment systems, telephones, and even auxiliary power for laptop computers and the like. If a seat is unoccupied, it may be desirable to disable or reduce the power supplied to the seat to conserve power for other passengers. In theory, passenger seat assignments might provide a framework for determining which seats on an aircraft are unoccupied. If a flight is not full, though, it is common for passengers to move from their initially assigned to seat to a more desirable open seat. There may also be appreciable periods of time when passengers are out of their seats, such as to visit the lavatory, when power to the seat can be shut off or minimized without significantly inconveniencing the passenger.
As noted above, automobile seats have been proposed which include passenger weighing apparatus to detect whether the seat is occupied. Including an entirely separate mechanism, the sole purpose of which is to determine the seat occupancy, can add undesirable weight to the seat. The temperature and pressure variations encountered in aircraft environments can also interfere with use of some of the passenger sensing systems proposed for automobiles, such as inflatable pressure-sensitive bladders.